The present invention relates to a method and device for decreasing the voltage over a dissipation-type voltage regulator.
In electronic devices and especially, but not necessarily, in wireless mobile communications devices, there are several different operating voltages, which are switched on and off according to the necessary functions. A long-lasting and small rechargeable voltage source has been a preferred feature in mobile communications devices and portable electronic devices in general. As circuit design technology has continuously developed, it has become possible to manufacture devices with a lower operating voltage than before. The development has also made it possible to reduce the size and weight of rechargeable power sources such as mobile phone batteries without significantly reducing the operating time of the device.
Both high and low-current operating states appear in mobile communications devices, where in high-current operating states especially the transmitter part consumes the most notable portion of the voltage source""s capacity. The power supply in a mobile communication device has traditionally been almost solely carried out with dissipation-type voltage regulators, also known as linear regulators, the only exception being some charge pump-type regulators meant for the RF part. In dissipation-type voltage regulators, the amount of current is regulated with a regulation circuit, which produces the required voltage dissipation between the input and output circuit (dV=Vinxe2x88x92Vout). The regulation circuit functions as the voltage-decreasing resistor R, which is connected in series with the load. The entire current load flows through it, creating power loss that is proportional to the square of the current load (Ploss=R*I2). A dissipation-type voltage regulator is outlined below using a linear regulator as an example. As a voltage regulator, the linear regulator solution is in itself simple and easy to implement and works well in low-current operating states such as when a mobile communications device is in idle mode, but with large current it causes the linear regulator and the whole device to overheat and lose voltage source capacity for instance during a call.
FIG. 1 illustrates a linear regulator, port 11 of which is connected to the voltage source, port 12 is connected to the ground. The input voltage Vin is between ports 11 and 12 and the linear regulator""s output voltage Vout is between ports 12 and 13. A voltage difference of at least dV must be left over the linear regulator to achieve the desired output voltage Vout. The value of the output voltage Vout is not dependent on how much Vin is larger than the minimum value (Vout+dV). Too small a voltage difference dV is also seen as a drop in the output voltage Vout, which may not be desired. The following example illustrates the growth of the linear regulator""s power loss as the current grows. The example uses the situations and values, where Vin=3.6 V, Vout=1.8 V, load current in idle mode Ia=5 mA and in call mode Ib=100 mA. The power consumed by the linear regulator in idle mode is Pa=9 mW and if we move to the said call mode, the linear regulator""s power consumption is now Pb=180 mW. The values illustrated above are only guidelines and only illustrate the fact that the current consumption in idle mode is usually a few milliamperes at most whereas in call mode the current consumption is several hundred milliamperes.
Several different solutions have been developed to minimise the energy consumption and thereby prolong the device""s operating time. One example is regulating the transmission power during transmission, which improves the operating time. However, this solution does not remove the problem noticeable in connection with regulating battery voltage as overheating of the linear regulator and device and as power loss.
A method and device have now been invented to decrease the voltage over a dissipation-type voltage regulator.
According to the first aspect of the invention, there is implemented a regulator coupling (FIG. 2) comprising a dissipation-type voltage regulator, which has an input for receiving input voltage (Vs) and an output for providing output voltage (Vout), and means (Vbat) for providing the said input voltage to voltage regulator, characterised in that the regulator connection consists of a first and second operating mode, means for providing the said input voltage with a first voltage value in the said first operating mode and means for providing the said input voltage with a second voltage value in the said second operating mode, in which the second voltage value is smaller than the said first voltage value.
According to a second aspect of the invention, there is implemented a method for using a dissipation-type voltage regulator, in which an input voltage (Vs) is formed for the voltage regulator and output voltage (Vout) is received from the voltage regulator, characterised in that the method uses the voltage regulator in a first and a second operating mode, a first voltage value is formed for the said input voltage (Vs) in the first operating mode, and a second voltage value is formed for the said input voltage (Vs) in the second operating mode, in which the second voltage value is smaller than the said first voltage value.
According to a third aspect of the invention, there is implemented an electronic device comprising at least one dissipation-type voltage regulator, which has an input for receiving input voltage (Vs) and an output for providing output voltage (Vout), and means for providing the said input voltage to voltage regulator, characterised in that the regulator coupling comprises a first and second operating mode, means for providing the said input voltage with a first voltage value in the said first operating mode and means for providing the said input voltage with a second voltage value in the said second operating mode, in which the second voltage value is smaller than the said first voltage value. The electronic device is preferably a mobile communications device.
The invention uses, depending on the load level of the dissipation-type voltage regulator, the best possible regulation method by combining the best assets of switched-mode-type and dissipation-type voltage regulators. When the load current is low, the linear regulator can be used on its own, because the heat and capacity losses are low even though the voltage over the linear regulator is high. When the load current is high, for instance during a call, a switched-mode-type voltage regulator is used to pre-regulate the voltage to such a level that the heat losses in the linear regulator after it are kept low. The output voltage of the linear regulator is always the same regardless of which regulation method is used. The switched-mode-type voltage regulator works as a power transformer, i.e. it does not lose as much battery capacity in heat losses. This is especially true with large load currents, in which case the efficiency of the switched-mode-type voltage regulator is at its best. With small current, on the other hand, the current consumption resulting from the connection loss of the switched-mode-type voltage regulator reduces the efficiency and its use is no longer justified.
With the invention, a simple means of reducing the voltage over the dissipation-type voltage regulator is achieved when using large load currents. The overheating and power loss of the voltage regulator in question is also reduced from what it was previously. Use of the method allows efficient utilisation of the voltage source""s capacity, due to which the same capacity grants a longer operating time than before. The invention also makes it possible to always use the best regulation method in various situations, because the transition from one mode to another does not cause a break in the linear regulator""s input voltage. Therefore, e.g. the transition from idle mode to call mode and vice versa in a mobile communications device can be performed smoothly.